Abstract: Tree plantations are globally significant, and therefore, growth-related challenges cannot be ignored. Canopy structure and light environment influence the growth of plantations, but the precise relationship remains unclear. We selected seven-year-old poplar plantations of varying cultivars planted various densities and measured their growth, canopy structure, and light environment. The findings indicate that poplar plantations of different cultivars and at different planting densities showed variations in leaf area index (LAI), average leaf angle (ALA), crown length (CL), length ratio (CLR), roundness (CR) and surface area (CSA), which directly or indirectly affect growth, resulting in disparities in their growing conditions. Crown roundness directly impacted growth, while LAI, CLR and ALA influenced growth indirectly by affecting intercellular carbon dioxide concentration. LAI and CLR had a positive effect; ALA had a negative one. Crown length and surface area directly and indirectly influenced growth by affecting photosynthetically active radiation and net photosynthetic rate, with direct impacts being more pronounced. This research has clarified the regulatory role of canopy structure in plantations growth, providing valuable insights for developing more effective management strategies.

Key words: Poplar growth, Photosynthesis, Hybrid clones, Structural equation modelling, Crown surface area